Fracture film for peelable membrane containers

ABSTRACT

The invention comprises a fracture film for sealing a peelable membrane to a container comprising a first layer of high density polyethelene, a second layer of polybutene-1/ethylene-vinyl acetate, wherein the second layer is bonded to the first layer, and a third layer of ethylene-acrylic acid, wherein the third layer is bonded to the second layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/365,523, entitled “FRACTURE FILM FOR PEELABLE MEMBRANE CONTAINERS,”filed Jul. 1, 2021, which is a continuation of U.S. patent applicationSer. No. 16/512,864, entitled “FRACTURE FILM FOR PEELABLE MEMBRANECONTAINERS,” filed Jul. 16, 2019, and is now issued U.S. Pat. No.11,084,249, each of which is incorporated herein in its entirety.

FIELD OF THE INVENTION

This invention relates generally to a fracture film for adheringpeelable membranes to containers.

BACKGROUND

A number of products, and particularly food products, are packaged incontainers wherein one of the container ends is closed with a thin,peelable foil membrane. The container is opened by peeling the foilmembrane from the end of the container to expose an opening into thecontainer. Such membranes typically comprise a flexible foil/polymercomposite structure which is heat sealed to a metal can end. Laminatedfoil membranes such as these often employ Surlyn® or other heat-sealingcoatings to adhere the membrane to the container end.

However, such foil membrane constructions have certain disadvantages.Surlyn® is an expensive sealant and suffers from the “age-up” phenomenonwhereby the strength of the seal to the metal end tends to increase withage, which is undesirable. This issue is particularly problematic in hotand/or humid environments, limiting global growth due to climateconcerns and a lack of climate-controlled warehousing. The age-upphenomenon causes the seal to become more difficult to peel away fromthe container over time. In some cases, the membrane actually transformsfrom a peelable seal to a “lock-up” seal that cannot be opened by aconsumer at all. The only way to manage this issue is to maintain strictcontrols over the initial seal strength via burst testing and pop/peeltesting, requiring container/membrane combinations to perform below theupper specification limits for the particular materials.

Surlyn® also has a relatively narrow heat-sealing temperature window. Ifthe temperature is too high, the seal strength will be too great toprovide easy peelability of the lid. Likewise, if the temperature is toolow, the seal strength may be too low to keep the lid from inadvertentlydetaching from the metal end. It can be difficult to control theprocessing conditions when using Surlyn® so as to stay within thedesired temperature window. Further, Surlyn® seals more readily tocertain types of metals than others and even for a given type of metalend, there can be substantial variability in the surface characteristicof the metal, which can affect the strength of the seal and thetemperature at which the seal must be processed. Such variability is notreadily predicted or accounted for, and hence the strength of the sealstends to have substantial variability. Accordingly, an alternativeclosure system has been sought.

SUMMARY OF THE INVENTION

It is desirable for a flexible membrane lid to be sealed to a containerend with sufficient strength to prevent inadvertent detachment of thelid during shipping and handling, prior to opening the container. On theother hand, it is also desirable for the consumer to be able to peel thelid off the container end with relatively little force, so that peopleof diverse ages and abilities can open the container, and so that thelid comes off in one piece rather than tearing. Through hard work andingenuity, the inventors have developed a product which reaches theseseemingly opposing objectives of high seal strength and low peel force.

In an embodiment, the invention is directed to a fracture film forsealing a peelable membrane to a container comprising a first layercomprising high density polyethelene; a second layer comprisingpolybutene-1/ethylene-vinyl acetate, wherein the second layer is bondedto the first layer; and a third layer comprising ethylene-acrylic acid,wherein the third layer is bonded to the second layer.

In another embodiment, the invention is directed to a containercomprising a bottom end; at least one sidewall extending upwardly fromthe bottom end and terminating in an open end; a peelable membranesealed to the open end of the at least one sidewall, wherein thepeelable membrane comprises at least one of the following layers: apolyethylene terephthalate layer; a foil layer; and a cast nylon layer;and wherein the peelable membrane comprises a fracture film whichcomprises: a first layer comprising high density polyethelene; a secondlayer comprising polybutene-1/ethylene-vinyl acetate, wherein the secondlayer is bonded to the first layer; and a third layer comprisingethylene-acrylic acid, wherein the third layer is bonded to the secondlayer.

In yet another embodiment, the invention comprises a method formanufacturing a container having a peelable membrane comprisingproviding a peelable membrane; providing a container having a metal end;coextruding a fracture film which comprises a first layer of highdensity polyethelene, a second layer of polybutene-1/ethylene-vinylacetate bonded to the first layer, and a third layer of ethylene-acrylicacid bonded to the second layer; laminating the high densitypolyethylene layer of the fracture film to the peelable membrane to forma laminate; cutting the laminate to fit the metal end; and inductionsealing the ethylene-acrylic acid layer of the laminate to the metalend.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the disclosure in general terms, reference willnow be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

FIG. 1 illustrates a perspective view of the container and membrane lidin an embodiment of the present invention.

FIG. 2 illustrates a cross-sectional view of the membrane lid andfracture film in an embodiment of the present invention.

FIG. 3 illustrates a cross-sectional view of the fracture film in anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings in which some but not allembodiments of the invention are shown. Indeed, the invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

As shown in FIG. 1 , in an embodiment, the invention comprises acontainer 10 to which a flexible membrane lid 20 is affixed. Theflexible membrane lid 20 may be affixed to the container 10 using afracture film 30. In an embodiment, an overcap may be applied to thecontainer over the flexible membrane lid 20. The overcap may be used toreclose the container after initial opening.

In an embodiment, the container 10 of the invention comprises metal. Inanother embodiment, however, the container of the invention may comprisepaper, plastic or any other material or combination of materials knownin the art. Likewise, the container 10 of the invention can be made byvarious processes. For instance, the container 10 can be formed ofplastic by thermoforming, blow-molding, or injection-molding, or can beformed of composite materials (e.g., paperboard with a liner ofimpervious material such as polymer film and/or foil) by spiral-windingor convolute-wrapping processes.

In an embodiment, the container 10 of the invention comprises a closedbottom end and at least one sidewall 12. The container may becylindrical, elliptical or ovular in nature or may have multiplesidewalls, comprising a generally rectangular or square cross-section,for example. Any container shape known in the art may be utilized. In anembodiment, the bottom end, sidewall(s) and top end generally form areceptacle having an interior which may house food products or the like.

In an embodiment, the end of the container 10 to which the flexiblemembrane 20 is affixed is the top end of the container. However, theflexible membrane 20 may be affixed to the bottom or a sidewall of thecontainer 10 in certain embodiments. In an embodiment, the end of thecontainer 10 to which the flexible membrane 20 is affixed may be metal,plastic, paper, or any combination thereof. In a particular embodiment,the container end is metal and comprises tin plated steel or aluminum.

In an embodiment, the container comprises a metal end 14 which is thetop of the container sidewall 12 or is attached to the top of thecontainer sidewall 12, optionally by double-seaming the metal end 14 toa flange at the top of the container. The metal end 14 may be referredto as a metal ring. Alternatively, the metal end 14 may be integral withthe container sidewall. In an embodiment, the metal end 14 may define anopening 16 into the container interior. The metal end 14 may comprise arim or flange to which the membrane lid 20 is sealed.

The flexible membrane lid 20 of the invention may be sealed to the metalend 14 so as to cover the opening 16 defined therein. The membrane lid20 generally includes one or more layers providing strength and/orbarrier properties. In an embodiment, the membrane lid 20 comprises anupper surface 22 proximate the exterior of the container and a lowersurface 24 proximate the interior of the container. In an embodiment,the membrane lid 20 comprises a fracture film 30 disposed on the lowersurface 24 of the lid. The function of the fracture film 30 is to sealthe membrane lid 20 to the metal end 14 and allow the membrane lid 20 torelease from the metal end 14 upon peeling back by a consumer.

In some embodiments, the fracture film 30 may be disposed over theentire surface lower surface 24 of the membrane lid 20. In anembodiment, the membrane lid 20 includes a pull tab 26 that is notsealed to the metal end 14 (i.e. does not have fracture film 30 disposedthereon) so that it can be readily grasped and pulled to remove themembrane lid 20 from the metal end 14.

In another embodiment, the fracture film 30 may be disposedcircumferentially or about the perimeter of the membrane lid 20. Thatis, the fracture film 30 may not cover the entire lower surface 24 ofthe membrane lid 20.

In an embodiment, the membrane lid 20 comprises multiple layers. In anembodiment the layers of the membrane lid 20 may comprise materials suchas metal foil, polymer films, metallized polymer films (i.e., filmhaving a very thin coating of substantially pure metal depositedthereon), paper, or any other materials known in the art. In anembodiment, at least one layer of the membrane lid 20 comprises abarrier layer. Various materials can be used as barriers, includingmetal foil, metallized polyester, non-metallized polymer film (e.g.,EVOH), and others. A combination of two or more such barrier layers canbe used.

In a particular embodiment, the membrane lid 20 comprises a layeredstructure which includes three layers. This embodiment should not belimiting, however, as any number of layers or composition of layers maybe utilized herein. In an embodiment, the membrane lid 20 comprises thefollowing three layers: polyethylene terephthalate (PET), a metal foil,and nylon. In an embodiment, the membrane lid 20 may comprise a layeredstructure as shown in FIG. 2 . In this embodiment, the outer layer 27 ofthe membrane lid 20 may comprise PET, the intermediate layer 28 of themembrane lid 20 may comprise a metal foil, and the inner layer 29 of themembrane lid 20 may comprise nylon. In an embodiment, the nylon layercomprises cast nylon.

In an embodiment, the PET layer comprises a PET layer which is betweenabout 45 and 50 gauge (ga) in thickness. In a particular embodiment, thePET layer may comprise 48 ga (½ mil). In an embodiment, the foil layermay be between about 0.5 and 1.5 mil in thickness. In a particularembodiment, the foil layer may be about 1.0 mil. In an embodiment, thecast nylon layer may be between about 70 and 80 ga in thickness. In aparticular embodiment, the cast nylon layer may be about 75 ga.

In an embodiment, the outer layer 27, intermediate layer 28, and innerlayer 29 may be adhered to each other using one or more adhesives, toform adhesive layers 40 between each layer. Likewise, an adhesive layer40 may be disposed between the inner layer 29 and the fracture film 30.Any adhesive known in the art, or any combination of adhesives known inthe art, may be utilized in this embodiment. In some embodiments, theadhesive may be a two-component adhesive. In other embodiments, theadhesive may be a single component adhesive. The adhesive may besolvent-based or solventless. In any case, the adhesive selected shouldhave adhesive forces which are stronger than the adhesive forces withinthe fracture film 30, to ensure that the separation of the peelablemembrane from the container end 14 occurs internally, within thefracture film 30, and not between any of the layers: outer layer 27,intermediate layer 28, inner layer 29, and/or fracture film 30. In anembodiment, the adhesive layer(s) 40 comprises a permanent adhesive.

In an embodiment, the fracture film 30 comprises a first layer 32, asecond layer 34, and a third layer 36. In an embodiment, the first layer32 is the top layer of the fracture film 30, which is adjacent the lowersurface 24 of the membrane lid 20. In an embodiment, the third layer 36comprises the bottom layer of the fracture film 30, which is adjacentthe metal end 14.

In an embodiment, the first layer 32 of the fracture film 30 compriseshigh density polyethelene (HDPE). The HDPE, in some embodiments, acts asa relatively stiff backbone for the fracture film 30. The HDPE layeradditionally benefits the manufacturing process by reducing curl andcausing the membrane lid 20/fracture film 30 lamination to be easier tocut (discussed below).

In an embodiment, the second layer 34 of the fracture film 30 comprisespolybutene-1/ethylene-vinyl acetate (PB-EVA). In an embodiment, thePB-EVA layer serves as the fracture layer of the fracture film 30. Thatis, the PB-EVA layer may be designed to weaken, fracture, and/or peelduring the removal of the membrane lid 20 from the metal end 14. In someembodiments, the PB-EVA layer serves as a tie layer. In someembodiments, the PB-EVA cohesively bonds the layers on either side ofit. In an embodiment, the ratio of EVA to PB in the PB-EVA layer may beapproximately 2:1 by weight. In an embodiment, the ratio of EVA to PB inthe PB-EVA layer may be less than or equal to 2:1 by weight.

In an embodiment, the third layer 36 of the fracture film 30 comprisesethylene-acrylic acid (EAA). In an embodiment, the EAA layer serves asthe contact layer or seal layer between the membrane lid 20 and themetal end 14.

In an embodiment, the fracture film 30 may have a thickness of betweenabout 1.0 and 2.0 mil. In another embodiment, the fracture film 30 mayhave a thickness of about 1.5 mil. In an embodiment, the layerdistribution of the fracture film 30 is approximately 70% HDPE,approximately 10% to 15% PB-EVA, and approximately 10% to 15% EAA.

In an embodiment, the first layer 32 is bonded to the second layer 34and the second layer 34 is bonded to the third layer 36. In anotherembodiment, the first layer 32 and third layer 36 are bonded via thesecond layer 34—that is the second layer 34 acts as a bonding agent forthe first layer 32 and third layer 36.

In an embodiment, the fracture film 30 is configured to fractureinternally upon peeling back of the membrane lid 20 by a consumer. In anembodiment, the second layer 34 of the fracture film 30 is configured tofracture internally upon peeling of the peelable membrane 20. In thisembodiment, a portion of the second layer 34 may remain adhered to thefirst layer 32 and a portion of the second layer 34 may remain adheredto the third layer 36.

In another embodiment, the fracture film is configured to separatebetween the second layer 34 and the third layer 36 upon peeling of thepeelable membrane 20. In still another embodiment, the fracture film isconfigured to separate between the second layer 34 and the first layer32 upon peeling of the peelable membrane 20. In an embodiment, at leasta portion of the third layer 36 remains on the metal end 14 afterremoval of the peelable membrane 20 by a consumer. In an embodiment, theentire third layer 36 remains on the metal end 14 after removal of thepeelable membrane 20 by a consumer. In an embodiment, at least a portionof the second layer 34 and the third layer 36 remain on the metal end 14after removal of the peelable membrane 20 by a consumer. In anotherembodiment, the entire second layer 34 and the entire third layer 36remain on the metal end 14 after removal of the peelable membrane 20 bya consumer.

In an embodiment, the remnants 50 of the second layer 34 and/or thirdlayer 36 (also referred to as the footprint 50) which remain on themetal end 14 after removal of the peelable membrane 20 by a consumer mayprovide a consumer with confidence that the seal was effective prior tohis or her opening of the container 10, providing a tamper evidencefeature. This footprint 50 may comprise a visible ring that remains onthe metal end 14. In other embodiments, the footprint 50 may comprise adiscontinuous visible ring.

By designing the peelability mechanism (i.e. the fracturing) into thefilm itself (i.e. in contrast to the peeling occurring between thesealant and the metal end), the present invention does not depend on theseal strength of the membrane lid to the metal end to determine totalseal strength, as the membrane is not designed to separate cleanly fromthe metal end. Rather, because the fracture film 30 of the inventionfractures internally, it can be utilized in combination with anypeelable membrane known in the art and any container end known in theart. The seal strength of the fracture film 30 defines the seal strengthof the closure, regardless of the particular peelable membrane orcontainer end utilized.

In some embodiments, the thickness of the various layers may be alteredto improve functional characteristics of the container structure. Forexample, if the EAA layer is provided in a thinner layer, the membranelid 20 has a lower peel force and may be easier to peel. Likewise, ifthe EAA layer is provided as a thicker layer, the peel force of thestructure will be increased and the membrane lid 20 may be moredifficult to remove. Similarly, if the PB-EVA layer contains greateramounts of PB, the resulting structure will require a lower peel forceand will be more easily peelable. Likewise, if the PB content isdecreased, the resulting structure may require a higher peel force andmay be more difficult to peel. Still further, the EAA layer may beinternally modified to affect functional characteristics of thecontainer construction. For example, if the amount of acrylic acidwithin the EAA layer is increased, the resulting membrane lid 20 willhave a greater affinity to the metal end 14 (or any end), creating amore effective seal. Likewise, if the amount of acrylic acid within theEAA layer is decreased, the resulting membrane lid 20 will have a loweraffinity to the metal end 14 (or any end), creating a less effectiveseal.

The closure system of the invention can be employed with various typesof metal ends, including bare (i.e., uncoated) metal as well as coatedmetal. As examples, the invention is applicable to spot-coatedelectro-tin-plated (ETP) steel as well as uncoated ETP steel. Theinvention is advantageous in that the blow-off strength and peel-forcecharacteristics of the seal between the peelable lid 20 and the metalend 14 are not affected to a substantial extent by the surfacecharacteristics of the metal end (i.e., whether it is uncoated orcoated, etc.) because the failure mechanism of the seal occurs withinthe fracture film 30.

In an embodiment, the membrane lid 20 has a holding force to the end ofthe can which is sufficient to reliably maintain vacuum and/or sealduring handling conditions, including packaging, shipping and longstorage of the cans, while concurrently being removable with a peelforce acceptable to a consumer of average strength.

Method of Manufacture

In an embodiment, the method for manufacturing the container of theinvention comprises formation of a fracture film as described herein. Inan embodiment, the fracture film is formed via a blown film line (i.e.blown film extrusion) or cast film line, as such methods are known inthe art. Likewise, the layers which comprise the peelable membrane lidare laminated together using a permanent adhesive. In an embodimentwherein the peelable membrane lid comprises three layers, an adhesivemay be applied to a first layer of the membrane lid and the first layermay then be adhesively joined to a second layer of the membrane lid. Anadhesive may be applied to a second layer of the membrane lid (or,alternatively to the third layer of the membrane lid) and the secondlayer of the membrane lid and the third layer may then be adhesivelyjoined to form a laminated membrane lid.

The fracture film is then laminated to the underside of the peelablemembrane lid using a permanent adhesive in a similar manner. Laminationmay be accomplished using a laminating machine comprising two rollersforming a nip therebetween, or may be accomplished using any othermethod known in the art.

In an embodiment, the fracture film is laminated to the underside of thepeelable membrane lid in sheet form, such that the fracture film iscoextensive with the peelable membrane. That is, the fracture filmcovers the entirety of the underside of the peelable membrane.

In an embodiment, the laminated film is then fed to a cutting stationwhere the film may be cut into discrete lids which are sized for aparticular container application. In an embodiment, the lids are cut toinclude a pull tab which extends from a side of the lid. In anembodiment, the lids are generally circular, with the exception of thepull tab. The lids may be cut with a laser, a die cutting machine or byany other suitable means known in the art. The skeleton of the laminatemay be removed and discarded.

In an embodiment, the cut membrane lids are then sealed to preformedmetal ends. In a particular embodiment, the membrane lid is inductionsealed to the metal end. In an embodiment, the metal end comprises aflange or ring to which the membrane lid is sealed. The inductionsealing process may comprise induction heating the metal end and thenapplying the lid to the heated end under pressure. In an embodiment, thesealing may occur at a temperature range of between about 250° F. toabout 500° F. for 1 second using pressure of about 40 PSI.

The fracture film will seal to the metal end. In an embodiment, thepeelability of the membrand lid may be altered based upon the processingconditions. For example, if more heat and/or pressure are applied duringthe induction heating process, the resulting container may have a lowerpeel strength and may be easier to peel. The converse is also true.

Many other modifications and other embodiments of the inventions setforth herein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A flexible membrane lid comprising: one or moreadjacent layers comprising metal foil, polymer film, metalized polymerfilm or paper; and a fracture film adhered to the one or more adjacentlayers comprising: a stiff layer; a fracture layer comprising a blend ofpolybutene-1/ethylene-vinyl acetate; and a sealing layer comprisingethylene-acrylic acid, wherein the fracture layer cohesively bonds thestiff layer and the sealing layer.
 2. The flexible membrane lid of claim1, wherein the stiff layer of the fracture film comprises high densitypolyethylene.
 3. The flexible membrane lid of claim 1, wherein thefracture film is sealed to a metal end of a container.
 4. The flexiblemembrane lid of claim 3, wherein the fracture film is configured tofracture internally upon peeling of the flexible membrane lid away fromthe metal end of the container.
 5. The flexible membrane lid of claim 4,wherein the fracture film is configured to separate at the fracturelayer such that a first portion of the fracture layer is bonded with thestiff layer, and a second portion of the fracture layer is bonded withthe sealing layer.
 6. The flexible membrane of claim 3, wherein uponpeeling of the flexible membrane away from the container, a footprint ofthe fracture film remains on the metal end.
 7. The flexible membrane ofclaim 6 wherein the footprint is one of a segment of the sealing layer,the sealing layer, the sealing layer and a portion of the fracturelayer, or the sealing layer and the fracture layer.
 8. The flexiblemembrane of claim 1, wherein the one or more adjacent layers includes afirst layer comprising polyethylene terephthalate; a second layercomprising foil adhered to the first layer; and a third layer comprisingnylon adhered to the second layer.
 9. The flexible membrane of claim 1,wherein the weight of ethylene-vinyl acetate in the fracture layer is upto twice the weight of polybutene-1 in the fracture layer.
 10. Afracture film for sealing a peelable membrane to a container comprising:a first layer comprising high density polyethylene; and a third layercomprising ethylene-acrylic acid, wherein the third layer is covalentlybonded to the first layer with a second layer comprising a blend ofpolybutene-1/ethylene-vinyl acetate, wherein the a blend ofpolybutene-1/ethylene-vinyl acetate is configured to fracture uponpeeling the peelable membrane.
 11. The fracture film of claim 10,wherein the fracture film is sealed to an end of a container.
 12. Thefracture film of claim 11, wherein a footprint is adhered to a metal endof the container upon peeling of the flexible membrane lid.
 13. Thefracture film of claim 12, wherein the footprint is one of: a portion ofthe third layer, the third layer, the third layer and a portion of thesecond layer or the third layer and the second layer.
 14. The fracturefilm of claim 10, wherein one or more adhered layers are adhered to thefracture film.
 15. The fracture film of claim 14, wherein the one ormore adhered layers comprise a polyethylene terephthalate layer; a foillayer adhered to the polyethylene terephthalate layer; and a nylon layeradhered to the foil layer.
 16. The fracture film of claim 10, whereinthe weight of ethylene-vinyl acetate in the second layer is up to twicethe weight of polybutene-1 in the second layer.
 17. The fracture film ofclaim 10, wherein the fracture film is comprised from at least 70% highdensity polyethylene, between 10% and 15% polybutene-1/ethylene-vinylacetate and between 10% and 15% ethylene-acrylic acid by weight.